The invention pertains to a device and a method for adjusting the height of a mold of a tire curing press, in which the mold comprises at least two mold parts positionable relative to each other.
The invention also pertains to a tire curing press with a mold comprising two mold parts positionable relative to each other and provided with a device for adjusting the height of the mold by changing the position of at least one of the mold parts.
According to the prior art, the height of the mold of a tire curing press is adjusted by the use of, for example, a spindle, the external thread of which engages in the internal thread of a nut. A tire curing press typically comprises a frame, and the mold parts are shifted in a vertical direction.
According to the prior art, the height adjustment is often carried out by the use of an electric drive and a gearbox. Thus, according to the prior art, a rotating type of drive is used, and the rotational movement is converted into a linear movement by means of the known principle realized by the engagement between the threaded spindle and the threaded nut. The linear movement of at least one mold part, i.e., of one of the two halves of the mold, which usually consist of a matrix and a patrix or of a matrix and a pressure disk, is necessary so that the clear width of the required opening, which depends on the dimensions of the tire to be produced and thus the height of the mold can be influenced during the tire production process.
Because of the considerable forces which arise during the production of a tire in a mold, the components, especially the mold parts being used, must have extreme dimensional stability. As a rule, this can be achieved only by making these mold parts, i.e., a matrix and a pressure disk, very massive. These components can thus be extremely heavy and very large.
The linear movement of these components by means of spindle-nut arrangements requires dimensions on a similar scale. So that the required forces can be transmitted, the size, thread type, and especially the materials must be selected so that these loads can be withstood. The choice of high-strength materials makes the machining process or the mass forming by rolling normally used to produce the threads on the spindle and in the nut much more difficult. The spindle and the nut thus become extremely labor-intensive and expensive.
Another problem is that, because of the considerable length of the spindle which is unsupported, the mechanical element consisting of the spindle and the nut are highly susceptible to buckling, especially at the end positions of their linear travel, when the unsupported length is at its maximum. This reduces the property to absorb the linear forces which must be taken up along the axis of the spindle.
The use of a spindle and nut inside the tire curing press is not a simple matter either. A threaded spindle and a nut are often difficult to install and to maintain. In addition, continuous lubrication is also required.
An additional problem is that the drive power-producing unit, i.e., the rotating electric drive in most cases, for the spindle-nut assembly must be arranged directly inside the tire curing press. If the width adjustment of the mold halves is provided on top of the upper mold half, as frequently realized in column-type curing presses, then the amount of space thus occupied must be taken into account, and every time the upper mold half is opened or closed, the rotary drive must be moved as well.